This invention is directed to vehicle suspension systems, and to linkage suspensions incorporating a unique linkage component. More particularly, the invention is directed to a four-point wishbone-shaped linkage suspension component and suspension systems incorporating a four-point wishbone-shaped linkage. This four-point wishbone-shaped linkage in combination with other suspension system components improves vehicle handling, axle control, ride comfort and cargo protection while minimizing the complexity, package space and weight of the suspension system.
Suspension systems suspend the vehicle chassis over the axle of the vehicle and absorb axle movement caused by the wheels encountering obstacles, holes and uneven road surfaces. Axle movement occurs not only when the wheels encounter obstacles in the road but also during acceleration and braking and during cornering (when the vehicle makes turns). In these situations, it is required that the suspension system provides stability to the vehicle by controlling axle movement.
Suspension systems utilize several different components in various configurations to control the range of axle motions. Leaf springs or beams are widely used components of suspension systems and play a major role in controlling certain axle motions. Leaf springs however, are expensive to manufacture and assemble, add significant weight to the suspension, and add to the overall complexity of the suspension when used in conjunction with a stabilizer bar for additional roll stability to achieve a desired vertical spring rate in a given suspension packaging envelope. When optimizing for ride comfort, a low vertical spring rate is desirable, however roll stability usually suffers especially in leaf spring suspension systems. Primary roll stiffness is directly proportional to the vertical spring rate of leaf spring suspensions. Therefore in order to provide the desired ride comfort characteristics, an auxiliary roll stiffness mechanism such as a stabilizer bar must be employed, which adds both cost and weight. Reducing the weight of the suspension system translates into higher payload capacity, in the case of commercial vehicles, and/or lowers fuel costs. U.S. Pat. No. 6,527,286, which is hereby incorporated by reference herein, discloses suspension systems that do not employ leaf springs. In the suspension systems disclosed by Keeler et al., the pair of leaf springs—one on each side of the axle—is replaced by a fabricated torque box along with other components.
While replacing the pair of leaf springs with a torque box can be readily accomplished in rear, tandem or trailer axles, there are issues unique to the front steering axle that makes incorporating the torque box configuration more difficult in steering axle suspension systems. First, there are packaging constraints. The space above and around the steering axle is typically occupied by the engine, cooling systems, and oil pan sump, among other things. This leaves limited space for the torque box, especially considering that the torque box will move up and down in conjunction with the axle.
Another issue relates to the kinematics involved in the steering axle. Assuming a torque box could be incorporated in a steering axle suspension system, there may be undesirable steering kinetics. For example, in a leading arm arrangement where the torque box is connected to the steering axle and frame and where the axle is ahead of the torque box linkages, the compliant nature of the bushing and bar arrangement of the torque box could cause an undesirable over-steer effect. Over-steer is when the vehicle turns into the bend or corner the driver is attempting to negotiate more than what was desired or expected. Under-steer effect is the opposite in that the vehicle does not turn into the bend as much as anticipated forcing the driver to take additional steering action to turn the vehicle. An under-steer condition is more desirable and safer than an over-steer condition since the driver feels more in control of the vehicle and since over-steer could contribute to a dangerous rollover condition.
In view of the forgoing, it is desirable to reduce the cost, weight and complexity of steering axle suspension systems. In particular, it would be desirable to replace the leaf spring components employed in many suspension systems while improving or at least not negatively affecting the performance of the suspension system. In addition, it would be desirable to provide a suspension assembly for steering axles having the benefits of a torque box configuration but without the adverse effects on steering kinetics that a torque box may cause. It would also be desirable to design such a suspension that fits within packaging limitations of the vehicle. Moreover, it would be desirable to provide a linkage component for use in a steering axle suspension assembly considering the limited packaging space around the steering axle. Furthermore, it would desirable if the linkage could also be used as a component of non-steering axle suspension systems.
The benefits of the preferred forms of the novel subject matter set forth herein will become apparent from the following description. It will be understood, however, that an apparatus could still appropriate the invention claimed herein without accomplishing each and every one of those benefits gleaned from the following description. The appended claims, not the benefits of the novel subject matter set forth herein, define the subject matter protected by law. Any and all benefits are derived from the preferred forms of the invention, not necessarily the invention in general.